Process for manufacturing sulfur dioxide by burning sulfur



Feb. 4, 1958 J. J. SHIPMAN ETAL PROCESS FOR MANUFACTURING SULFUR DIOXIDE BY BURNING SULFUR 4 Sheets-Sheet 1 Filed NOV. 26, 1954 Feb. 4, 1958 J. J. SHIPMAN ET AL 2,822,245

PROCESS FOR MANUFACTURING SULFUR DIOXIDE BY BURNING SULFUR 7 Filed Nov. 26, 1954 4 Sheets-Sheet 2 I 1 l M" w I N I i R w I I1 51 M; II H 1 23 '1 1953 J. J. SHIPMAN ET AL 2,822,245

PROCESS FOR MANUFACTURING SULFUR DIOXIDE BY BURNING SULFUR Filed Nov. 26, 1954 '4 Sheets-Sheet 3 Q Wnnzeqa 1958 J. J. SHIPMAN ET AL 2 PROCESS FOR MANUFACTURING SULFUR DIOXIDE BY BURNING SULFUR Filed Nov. 26, 1954 4 Sheets-Sheet 4 nun pun PROCESS FQR MANUFACTURING SULFUR DIOXIDE BY BURNING SULFUR Application November 26,1954, Serial No. 471,156

Claims. (Cl. 23-179) The present invention is related generally to-the manufacture of sulfur. dioxide gas and, more particularly, it relates to methods and apparatus for burning sulfur in relatively small, compact units.

For many years, sulfur dioxide has been prepared by burning sulfur and, sulfur dioxide so produced has been widely used in the paper industry, primarily for the manufacture of. sulfite pulp; in the food industry, as a preservative and forother' purposes; and in many other industries for preservation, fumigating, tanning, and a variety of other purposes.

Several different types of equipment are available for preparing sulfur dioxide by burning sulfur. In general, this. equipmentcomprise-s means for melting or vaporizing solid sulfur, the liquid or vapor being then pumped to a combustion chamber. wherein the sulfur is, of course, burned. It has been: thought, heretofore, that the burned gases must be retained at a high temperature for a sub stantial period of time in order to completely oxidize the sulfur to sulfur dioxide.

Accordingly, it has been considered necessary in the design of sulfur burners. to use very large combustion chambers in order toprovide sufficient time for the chemical reaction of sulfur and oxygen. to form sulfur dioxide. In fact, it has been an accepted: principle in the design of sulfur burners that the larger the chambers the better the design. In this connection, sulfur. burners have been rated by the' volume of the chambers relative to the amount of sulfur burned in a particular time. Specifically, burners have been rated in terms of cubic feet of combustion chamber volume per ton of. sulfur burned per day, and. it has. been generally considered desirable that the rating"v of. the chamber should be not less than; 25 cubic feet per ton perday, and that ratings up to 60-cubic feet per. ton. per day were both practical and desirable; such ratings being believed necessary to providesufiicient time for the: chemical reaction of sulfur and oxygen.

To illustrate, 21 Glen Falls rotary burner, which is a standard sulfur burner employed in the paperindustry, has a combustion; ohamben rating. of 60 cubic feet per ton per day. Another. widely. usedindustrial installation has: arating of- 46- cubic feet per ton per day While still another has a. rating of 28- cubic feet per ton per day. We are not aware of any industrialsulfuri burners having a rating of less than about. 25 cubic feet-.perton per day. it. will be noted that the. ratingof a burner. does-not refer to its output but, as indicated,, relates to the volume of the combustion chamber per ton ofsulfur' burned per day.

The use of such: larg. combustion: chambers not only requires substantial capital investment, space, and maintenance but alsoinherently resultsinuneconomies due to considerable heat. losses. Further-more, suclr large units. have. deterred. many users. of sulfur? dioxide from manufacturing the gas and, as a result,..they haveh'adt to buy the gasin tank cars. and incylinders,- the gasusually 2,822,245 Patented Feb. 4, 1958 2 being under pressure. The disadvantages of purchasing sulfur dioxide in tank cars and in cylinders is readily apparent from the point. of View of the high cost of the product, the cost of handling the cylinders and tank cars and, in. addition, such handling tends to'be an industrial hazard.

In order not toincrease the size of. combustion charm bers, in accordance with the heretofore accepted principles of. sulfur burner design, it was considered: advantageous to decrease the velocity of the burned gas through the cornbustionchamber. However, the reduced velocity did not provide most satisfactory burning and it was found necessary to flow the gas through: a tortuous path Whichcaused relatively rlar-geeddy currents to be: established; In. other. words, the burned gases: were passed through the combustion chamber at a relatively slow rate and were mildly agitated during such passage. This is the type of burning-which has been believed necessary here tof'ore toassure satisfactory production of sulfur dioxide.

The establishment of the tortuous path required the use. of bafiles, checkerwork, or the like,.in the path'of the hot gases which, of course,.have relatively. *shortlife and cause maintenance problems; In this connection, it should be realized that the" gas temperatures in the com bustion chamber may be as high as 2700 F.

in addition to providing large combustion chambersand tortuous paths", further. attempts have been made to improve the production of sulfur dioxide by provision of various atomizers or nozzles but the principle that a long reaction timeis required to provide maximum pro duction of sulfur dioxide has: been generally adhered to in all suchwork and, as a consequence, the size or the combustion chambers has continued to be very large and; as previously noted, even larger chambers have been considered desirable.

The net result of the accepted sulfur burner design principles has been that the existing equipment is ex pensive, space-consuming and cumbersome. However, the existing equipment is diflicult to operate and to ad justtoyaryi'ng rates of'operation; Also, the large units are difficult to start up and shut down.-

As above" indicated, in conventional sulfur burning equipment available prior to the present. invention, the sulfur is melted orvap'ori'zed prior to: injection or feeding into the nozzle for burning; Solid sulfur has'not' been burned directly in industrial equipment, to immediately provide sulfur dioxide because of the inability of present equipment to efficiently burn solid sulfur directly to' sulfur dioxide. Accordingly, present installations include melting tanks or other auxiliary apparatus to melt the sulfur or vaporize the sulfur.

The principal object of the present invention is to overcome the. foregoing and other deficiencies of existing sul fur burners and to provide an improved method and apparatus for burning sulfur, Whether. in the form of solid, vapor, or liquid, so asto efiiciently produce sulfur dioxide. A more particular. object of the invention isto. ac.- complish such burning ina relatively small, compact unit; As will become more apparent hereinafter, the accomplishment ofthese and other objects of the invention is basedonthediscovery that the establishment of a mass velocity, with turbulent mixing, in a combustionv cham'rher in excess of one thousand (1,000) pounds" of total gas per hour per square foot of cross sectional area dur ing the period ofcombustion makesipossible greatly'improved. conditionsand" apparatus for the burning: of sul; fur- In general, the improvements of this invention. are accomplished by controlling the" burning; gases in a: par= ticula-r mannen this mariner being. contrary to the teachings of the art.

Various of the features of the invention are shown in the attached drawings in which:

Figure l is a side view, partially in cross-section, of apparatus in accordance with the invention, the apparatus being particularly adapted to use molten sulfur.

Figure 2 is a plan view, also partially in cross-section, of the apparatus shown in Figure 1.

Figure 3 is a side view, partially in cross-section, of another apparatus in accordance with the invention, this apparatus being particularly adapted for using sulfur provided by a rotary burner, a portion of which is shown in this figure.

Figure 4 is a plan view of the apparatus shown in Figure 3.

Figure 5 is a perspective view of a mixer which is used in the apparatus shown in Figures 3 and 4.

. Figure 6 is a schematic side view, in cross-section, of a conventional apparatus for burning sulfur.

Figure 7 is a plan view of apparatus of the type shown in Figure 6.

Figure 8 is a schematic side view, partially in crosssection, of another conventional sulfur burning unit.

As above pointed out, the principles of this invention are accomplished by effecting turbulent mixing of gases at a very high mass velocity, specifically in excess of one thousand (1,000) pounds of gas per hour per square foot of cross section during the combustion period, i. e. until substantially complete formation of sulfur dioxide has occurred. (The term mass velocity" is a well understood chemical engineering term, generally designated by the symbol G, and, as its units indicate, is the weight of gas per unit of time, flowing through a specified area which extends generally perpendicular to the direction of flow.) In conventional sulfur burning equipment, the mass velocity in the equipment is usually below about one hundred (100) pounds of gas per hour per square foot of cross section. This discovery of the more efficient burning of sulfur at high mass velocities is not only a signiflcant departure from present commercial practices, but, in addition, the teaching of high mass velocities for sulfur burning is contrary to the teachings of the art which teachings result in low mass velocities. We have found that through the use of turbulent mixing and high mass velocities, the sulfur can be burned in solid, liquid or vapor forms with high eificiency, and consequently, it is possible to eliminate the use of melting and vaporizing equipment.

Because of this discovery of effecting turbulent mixing at high mass velocities, it has been found that burning of sulfur can be effected in chambers which are one-thirtieth the size of the combustion burners believed necessary to accommodate various industrial operations. Furthermore, this discovery permits the design of equipment which can be adjusted for operations having relatively widely varying requirements. In other words, one installation can be utilized for producing substantially different amounts of sulfur dioxide. In effecting the high mass velocities of the invention, the ratio of the amount of air to the amount of sulfur (on a weight basis) should be at least about 4.3 and should not exceed about 13. At such ratios of air to sulfur, and at given feed rates, the cross-sectional area of the combustion chamber may be determined to provide the desired mass velocity.

While we have specified mass velocities of more than one thousand (1,000) pounds of gas per hour per square foot of cross-sectional area, substantial higher mass velocities are preferred, and, in this connection, mass velocities in excess of eight thousand (8,000) have been commercially used in the practice of our invention. It will thus be seen that the output of unit may be increased eight times over its minimum operating condition by increasing the mass velocity. This gives substantial'flexibility in operation, which flexibility has not been provided by previously known sulfur burning equipment.

While even higher mass velocities than eight thousand (8,000) pounds of gas per hour per square foot of crosssection may be used, the cost of establishing such higher velocities may become excessive. In other words, the higher mass velocities require higher pressure drops and the cost of such pressure drops may exceed the value of the benefit of using higher mass velocities.

As above stated, the gases must be in turbulent flow during burning. Such turbulence may be effected in various ways and, in this connection, it may be accomplished by variations in nozzle design, the design of the combustion chamber, and the manner of mixing gases in the combustion chamber. We have found, however, that at higher mass velocities, the desired turbulence is effected independently of nozzle design and the design of the combustion chamber. However, at lower mass velocities, in accordance with this invention, it is desirable to increase the turbulence of the burning gases by the use of special mixing nozzles, by formation of agitating means within the combustion chamber, and by introducing secondary air in particular ways to increase turbulence. It will be understood, however, that such turbulence increasing means are particularly of value at the lower mass velocities, e. g. mass velocities below about two thousand (2,000) pounds of gas per hour per square foot of crosssectional area. In general, therefore, the burning chamber may comprise a plain tubular chamber and simple nozzles may be employed with admission of air in any manner, provided that it is substantially uniformly distributed during burning.

Turbulent mixing, as used in this specification, refers to the maintenance of a state of fluid turbulence prior to burning and for the hot gases to be in a state of fluid turbulence at least equivalent to a Reynolds number of 5000. This assures that sulfur is reacted and that the gas does not contain unreacted sulfur and air at the end of the chamber, such condition being necessary to the satisfactory production of sulfur dioxide. In this connection, the combustion chamber may be extended to assure complete burning of sulfur, and we have found that the length of the combustion chamber need not be more than four times the length of the flame in the burner to provide satisfactory operations.

As is Well known, the Reynolds number is directly proportional to the diameter of the duct or chamber and the velocity of the gas through the chamber. It is also related to viscosity and, for purposes of determining Reynolds numbers, a viscosity of .0575 centipoises (17 percent sulfur dioxide at 2400 F.) is used.

Since the velocity is inversely proportional to the square of the radius of the chamber, for a given rate of flow, the smaller the diameter, the larger the Reynolds number and the higher the mass velocity. It will thus be seen that the smallness of the diameter of the chamber is an important feature of the invention for assuring turbulent mixing and high mass velocity.

As above indicated, the principles of the invention, above set forth, have made possible the construction of sulfur burners having an output equivalent to existing equipment but having a burning chamber which is a small fraction of the size of such equipment. Furthermore, by reducing the size of the chambers, the surface area is reduced so that heat losses can be reduced and gas temperatures remain higher. In addition, such size reduction permits more rapid establishment of operating conditions so that the burner of this invention can be more rapidly started up than conventional equipment. Accordingly, the equipment of the invention is more adaptable to commercial processes having intermittent sulfur dioxide requirements.

While various baflie, grid and vane structures may be provided for effecting turbulent mixing, the present invention includes the discovery of means whereby highly satisfactory operation can be achieved without such baffle structures and vane arrangement and whereby substantially smooth walled chambers may be used. This ,provides a substantial advantage from a maintenance view point, as well as from the point of view of initial cost. Because of the fact that the combustion chamber can be smooth walled, localized overheating will be substantially prevented, and similarly, no points of accumulation of dirt or sediment are provided. In addition, cleaning of such smooth walls is a relatively easy task and efficient recovery of heat can be easily effected.

The burning chamber may extend in a vertical direction or in a horizontal direction, or it may extend at some intermediate angle. Thus, the equipment design is very flexible and can be arranged to accommodate various manufacturing plants and industrial processes and operations.

Now referring to the drawings, Figures 1 and 2 illustrate apparatus of the invention which is in commercial operation for converting two and one-half tons of molten sulfur per day into sulfur dioxide, the apparatus including a nozzle section 13 into which is fed air, through pipe 15, and molten sulfur, through pipe 17. In order to maintain the sulfur in molten condition, the nozzle section is surrounded by a steam jacket 19, into which jacket steam is delivered through pipe 19:: and condensate removed through pipe 1911. The apparatus also includes a cylindrical combustion chamber 21, located immediately downstream from the nozzle section 13, which defines a generally L-shaped path and which comprises a casing 22 lined with refractory material 23. The chamber 21 has substantially smooth walls and is free from baffles, vanes, or the like, and includes a leg 21a which communicates with the nozzle section and another leg 21!; which feeds into a sulfur dioxide gas recovery unit (not shown). The leg 21a of the combustion chamber which communicates with the nozzle section 13 is about ten feet in length and it connects to the leg 21b which is about five feet long. Surrounding the casing 22 are jackets 25 through which air for burning is drawn, the air being pre-heated by the casing 22.

As shown in Figure 1, the leg section 21a of the combustion chamber 21 includes an enlarged section 210 located immediately downstream of the nozzle section 13 and a section of reduced diameter 21a" which communicates with the enlarged section 21a. The diameter of the enlarged section 21a is twelve (12) inches and it extends approximately 36 inches down the chamber 21. The section of reduced diameter 21a" is eight (8) inches in diameter and it connects to the leg 2112 which is also eight (8) inches in diameter.

Enlargement of the section of the combustion chamber immediately downstream of the nozzle is desirable in low capacity burners; in which burners the cross-sectional area is quite small. Such enlargement increases the surface area, and consequently, increases radiation back into the chamber which results in more improved burning. In general, with low capacity burners having small diameters and at mass velocities up to about five thousand (5,000), the enlarged section of the combustion chamber should have a diameter of about twelve (12) inches and should extend about three feet down the chamber from the nozzle to effect most satisfactory burning. The enlargement, in addition to effecting more improved burning, results in more uniform burning conditions.

As shown in Figures 1 and 2, air ducts 27, 28 and 29 communicate with the combustion chamber 21 downstream of the nozzle section 13 and these ducts converge away from that section, i. e. the ducts converge in the downstream direction. In the illustrated embodiment, the air ducts 27, 28 and 29 are each two inches in diameter and ducts 27 and 28 are located about two inches downstream of the nozzle section 13, duct 29 being twenty inches downstream of the nozzle section. The ducts 27, 28 and 29 converge at an angle of 60 degrees relative to the axis of the chamber. These ducts 27, 28 and 6 29 connect to a blower .31 through lines 32 the blower 31 receiving preheated air from the jackets 25 through ducts 33.

The overall length of the combustion chamber is fifteen (15) feet but the sulfur is substantially completely converted to sulfur dioxide in the first six feet of the chamber 21. We have provided the extra length to adapt the apparatus for any variation in burning conditions which might occur.

The burner gas and sulfur dioxide which are produced exit from the leg 21]) of the combustion chamber 21. Recovery of the sulfur dioxide gas is accomplished in accordance with well known practices and apparatus for effecting such recovery is not shown in the drawings.

As above set forth, the described apparatus is capable of converting two and one-half tons of sulfur to sulfur dioxide in 24 hours. In operation, sulfur, in molten form, is fed into the nozzle section through the tube 1'7 and atomizing air through tube 15, the ratio of sulfur to atomizing air being 8 to l, on a weight basis. Additional air is fed into the chamber 21 through the ducts 27, 28 and 29 under a pressure of three inches of Water. Heating steam is introduced into pipe 19 under a pressure of sixty pounds per square inch.

The equipment shown in Figures 1 and 2 is capable of etficiently handling from about three-quarters to about two and one-half tons of sulfur per day (24 hours). In the combustion chamber, the mass velocity may be from about 1,100 to about 3,900 pounds of gas per square foot er hour. With sulfur feed rates of two and one-half tons per day and with air feed at the rates specified, the Reynolds number is 18,000 in the combustion chamber 21a.

In the embodiment shown in Figures 1 and 2, the volume of combustion chamber per ton of sulfur burned or rating is less than seven cubic feet per ton of sulfur per day under minimum operating conditions while at optimum conditions the rating is about two cubic feet per ton of sulfur per day, even considering the extra volume provided for variations in burning conditions. This embodiment has the same capacity as the unit shown in Figure 8, which represents one presently employed commercial unit. This unit comprises a feed pipe 41 which feeds sulfur into a rotary burner 43. From the rotary burner, the sulfur vapor and other gases are fed into a generally cylindrical combustion chamber 4-5 wherein the sulfur vapor is burned. For the purposes of handling two tons of sulfur a day, the combustion chamber is, in the commercial embodiment, six feet high and five feet in diameter, so that the volume required per ton of sulfur is almost sixty cubic feet per ton of sulfur burned per day.

It will be seen from the foregoing that the principles of the invention provide a very much more compact unit for producing sulfur dioxide than has been available heretofore. In fact, it will be seen from the foregoing that the size of the combustion chamber may be one-thirtieth the size of a corresponding conventional unit. This is further illustrated by the apparatus shown in Figures 3 to 7, inclusive, of the drawings, which also illustrate the facility with which the principles of the invention can be applied to existing equipment. These figures illustrate how a combustion chamber of the invention can be substituted for a combustion chamber having a high rating.

Figures 6 and 7 illustrate a conventional apparatus for producing sulfur dioxide from sulfur, which apparatus is generally known as a rotary burner with an auxiliary combustion chamber. This apparatus comprises a sulfur feed pipe 51 which feeds molten sulfur into a hot rotary burner 53. Enough air is admitted to the burner to effect vaporization of the desired amount of sulfur. The sulfur vapors are delivered to a combustion chamber 55 with more air which comes through the damper 54 and burned. In the chamber 55 is disposed a baffle 56 (Figure 6) which is built up from refractory materials. The sulfur 7 dioxide passes around the bafl'le and is discharged through the exhaust duct 57. In some commercial installations, checkerwork or grids are substituted for the baffle.

In a commercial installation of the type shown in Figures 6 and 7 for handling seventeen tons of sulfur per day, the chamber is eight feet in diameter and sixteen feet in height so that the volume required for each ton of sulfur is about thirty cubic feet per ton of sulfur (which takes into account the volume occupied by the brick work of the baflie).

Figures 3 and 4 illustrate apparatus which is adapted for handling the output of a rotary burner and which can be and, in a commercial operation, has been substituted for the chamber 55 shown in Figures 6 and 7. As illustrated, the apparatus includes a combustion chamber 59 and a cylindrical nozzle section 61 which fits onto the discharge end 63 of a rotary burner 65. The nozzle section 61 comprises a mixer 64 which is formed as shown in Figure 5, the mixer being formed so as to give more area for mixing and to give the air and sulfur vapor mixture a swirling motion. The mixer 64 is hollow and generally clover leaf shape in cross-section and enlarges in the downstream direction. Vapors and gases from the burner 6% pass through the internal part of the mixer 64, and air passes over the outside of the mixer, the vapors and air mixing together at the downstream end of the mixer 64. The air which passes over the mixer enters the nozzle section 61 through a damper 66 located at the upstream end of the mixer. The damper 66, of course, may be adjusted to control the amount of air entering the nozzle section.

The combustion chamber 59 is generally cylindrical and comprises an outside casing 67 which is lined with refractory material 69. The chamber connects to suitable exhaust ducts 71. If the apparatus shown in Figures 3 and 4 is to be employed to convert seventeen tons of sulfur per day to sulfur dioxide, the combustion chamber 59 may be twenty inches in diameter and may extend from the nozzle section of the rotary burner about twelve (12) feet.

In operation of the apparatus shown in Figures 3 and 4, at seventeen tons of sulfur per day, air is fed to the rotary burner 65 at the rate of 25,000 cubic feet per hour under a pressure drop of about one and one-half inches of water. The Reynolds number in the combustion chamber 59 is 50,000. The mass velocity in the combustion chamber is over 4,000 pounds per square foot of cross-section per hour and should be compared with the mass velocity of 100 pounds per square foot of cross-section per hour in the apparatus shown in Figures 6 and 7 above described.

It will be seen that the combustion chamber has a volume of less than one and one-half cubic feet per ton of sulfur and is approximately one-twentieth the size of the corresponding conventional unit.

The apparatus shown in Figures 3 and 4 with the dimensions above specified can handle efiiciently sulfur at the rate of between about five tons per day to about thirty-five tons per day. Thus, the unit has substantial flexibility.

As has been previously pointed out, solid sulfur may be conveyed to the combustion chamber and burned in accordance with the principles of this invention. When solid sulfur is used, fine sulfur particles, 80 percent of which preferably pass through a forty mesh screen, should be employed. The sulfur should be conveyed to a combustion chamber by air, the amount of air being less than that required for burning and also less than that at which an explosion might occur. Specifically, in feeding sulfur to the combustion chamber, the ratio of air to sulfur should be between 1/3 and 3, on a Weight basis. In the combustion chamber, suflicient air must be provided to assure burning and to establish a mass velocity in excess of one thousand (l,000).pounds of gas per square foot of cross-section per hour. Overall, the ratio of air to sulfur should be in the range of from about 4.3 and about 13. Other than the equipment for conveying sulfur to the combustion chamber, which equipment is commercially available, the combustion chamber should be constructed in accordance with the above described specifications.

Any of the above described combustion chambers may be employed with sulfur coming into the chamber in the form of liquid, vapor or solid. Of course, the nozzle or feed mechanism must be selected to accommodate the form of sulfur being delivered.

As above indicated, various types of nozzles may be employed and, in this connection, only the simplest nozzle type has been illustrated. The principal gain with more complicated nozzles is in effecting improved turbulence at lower mass velocities.

Similarly, various modifications in the manner of introducing gas to the combustion chamber are possible, one such being shown in Figures 3, 4 and 5. This aids in increasing turbulence. Mixing may also be facilitated by the use of vanes or baffles in the combustion chamber. As above indicated, the use of such arrangements is generally to be avoided because of maintenance difficulties. However, these arrangements aid in further reducing the length of the combustion chamber because of the increased turbulence and may be desirable in particular installations.

The gas produced in accordance with the principles of the invention may be cooled after leaving the combustion chamber, and conducted to various industrial processes and operations. Cooling and transference of the gas is practiced in accordance with known procedures and are not described herein.

It has been found that in the above described apparatus of the invention, when the gas is handled by known procedures after burning, the content of sulfur trioxide may be less than one-half percent. This represents highly eflicient operation and is equivalent to or less than the amount of sulfur trioxide in gas produced by presently available sulfur burning equipment.

The principles of this invention can be applied in designing many different forms of apparatus to handle small or large amounts of sulfur and to provide units for widely varying requirements. In this connection, it has been found that for a given burner, the length of the flame divided by some critical dimension of the combustion chamber is proportional to the velocity of the sulfur and air fed at low rates, but as the feed rate increases and turbulent mixing occurs, the ratio of the length of the flame to the critical dimension is constant. This occurs at all ratios of sulfur to air in the combustion range. It will be apparent that when the sulfur and air are fed in proper proportion through a tube, the diam eter of the combustion chamber can be adjusted to provide a given flame lengthwhere turbulent mixing occurs. However, by variations in nozzle and combustion chamber design, the point where the ratio of flame length to diameter becomes constant may vary. The discovery of the constant ratio at and above a critical velocity is a reason for the compactness of the apparatus of the invention and assures optimum enjoyment of the invention.

In summary, the present invention provides an improved apparatus and method for burning sulfur in the form of vapor, liquid, or solid. As a result of this improvement, sulfur dioxide can be efiiciently produced in apparatus which is small and compact as compared to presently available equipment. This has made available sulfur burning equipment for small, as well as large, operations. Furthermore, the sulfur dioxide can be produced with minimum maintenance costs, as well as operational expenses. In addition, the apparatus and method of the invention provide flexibility in operation so as to make sulfur burning more adaptable to many industrial installations.

The various features of the invention which are believed to be new are set forth in the following claims.

We claim:

1. A process for manufacturing sulfur dioxide by burning which comprises feeding air and sulfur to a smooth walled tubular combustion chamber at such a rate as to establish a Reynolds number in excess of 5000 and a mass velocity in said chamber in excess of 2000 pounds per square foot per hour, forming said smooth walled combustion chamber with a limited length and with freedom of obstruction within said limited length whereby heat losses from said combustion chamber are minimized, the ratio of the weight of air to the weight of sulfur being in the range of from about 4.3 to about 13, subjecting the air and sulfur to turbulent mixing, burning the mixed air and sulfur while maintaining turbulent mixing until the sulfur is substantially completely converted to sulfur dioxide.

2. A process for manufacturing sulfur dioxide by burning which comprises feeding air and sulfur to a smooth walled, tubular combustion chamber, burning the mixed air and sulfur, the air and sulfur being fed at a fixed weight ratio in the range of from about 4.3 to about 13 and at such a rate that the flame length is substantially constant, independently of variations in the rate of sulfur feeding at said ratio, forming said smooth walled combustion chamber with a limited length which is at least as long as the flame and with freedom of obstruction within said limited length whereby heat losses from said combustion chamber are minimized.

3. A process for manufacturing sulfur dioxide by burning solid sulfur which comprises the steps of feeding solid sulfur into a smooth walled, tubular combustion chamber, feeding air to said chamber in an amount in excess of that required to burn said sulfur, the ratio of the weight of the air to the weight of sulfur being in the range from about 4.3 to about 13, the air and solid sulfur being fed into said chamber at such a rate as to establish a mass velocity in excess of 2000 pounds per square foot per hour, subjecting the air and sulfur to turbulent mixing, burning the mixed air and sulfur while maintaining turbulent mixing until the sulfur is substantially completely converted to sulfur dioxide, forming said smooth walled combustion chamber with a limited length and with freedom of obstruction within said limited length whereby heat losses from said combustion chamber are minimized.

4. A process for manufacturing sulfur dioxide by burning solid sulfur which comprises the steps of conveying solid sulfur to a smooth walled, tubular combustion chamber by air, the amount of air being sufiicient to convey said sulfur, but less than the amount which would support an explosion and less than the amount required for burning, said amount of air being more than times the weight of sulfur and less than 3 times the weight of sulfur feeding additional air to said combustion chamber in an amount in excess of that required to burn said sulfur, the total weight of said conveying air and said additional air having a ratio to the weight of sulfur in the range of from about 4.3 to about 13 the air and solid sulfur being fed at such a rate as to establish a Reynolds number in excess of 5000 and a mass velocity in excess of 2000 pounds per square foot per hour, subjecting the air and sulfur to turbulent mixing, burning the mixed air and sulfur while maintaining turbulent mixing until the sulfur is substantially completely converted to sulfur dioxide, forming said smooth walled combustion chamber with a limited length and with freedom of obstruction Within said limited length whereby heat losses from said combustion chamber are minimized.

5. A process for manufacturing sulfur dioxide by buming solid sulfur which comprises the steps of feeding solid sulfur of a size such that percent of the sulfur is smaller than about 40 mesh to a smooth walled, tubular combustion chamber by conveying air, the amount of conveying air being more than /3 times the weight of sulfur and less than 3 times the weight of sulfur, feeding additional air to said chamber in an amount in excess of that required to burn said sulfur, the total weight of said conveying air and said additional air having a ratio to the weight of sulfur in the range of from about 4.3 to about 13 the air and solid sulfur being fed at such a rate as to establish a Reynolds number in excess of 5000 and a mass velocity in excess of 2000 pounds per square foot per hour, subjecting the air and sulfur to turbulent mixing, burning the mixed air and sulfur while maintaining turbulent mixing until the sulfur is substantially completely converted to sulfur dioxide, forming said smooth Walled combustion chamber with a limited length and with freedom of obstruction within said limited length whereby heat losses from said combustion chamber are minimized.

References Cited in the file of this patent UNITED STATES PATENTS 1,473,879 Rudolf et al. Nov. 13, 1923 1,720,742 Mullen July 16, 1929 1,917,693 Bencowitz July 11, 1933 1,923,866 Hechenbleikner Aug. 22, 1933 2,310,173 Chatelain et al Feb. 2, 1943 2,705,671 Bencowitz Apr. 5, 1955 OTHER REFERENCES Conroy et al.: Industrial and Engineering Chemistry, vol. 41, No. 12 (December 1949), pages 2741-2748. 

1. A PROCESS FOR MANUFACTURING SULFUR DIOXIDE BY BURNING WHICH COMPRISES FEEDING AIR AND SULFUR TO A SMOOTH WALLED TUBULAR COMBUSTION CHAMBER AT SUCH A RATE AS TO ESTABLISH A REYNOLDS NUMBER IN EXCESS OF 5000 AND A MASS VELOCITY IN SAID CHAMBER IN EXCES OF 2000 POUNDS PER SQUARE FOOT PER HOUR, FORMING SAID SMOOTH WALLED COMBUSTION CHAMBER WITH A LIMITED LENGTH AND WITH FREEDOM OF OBSTRUCTION WITHIN SAID LIMITED LENGTH WHEREBY HEAT LOSSES FROM SAID COMBUSTION CHAMBER ARE MINIMIZED, THE RATIO OF THE WEIGHT OF AIR TO THE WEIGHT OF SULFUR BEING IN THE RANGE OF FROM ABOUT 4.3 TO ABOUT 13, SUBJECTING THE AIR AND SULFUR TO TURBULENT MIXING, BURINING THE MIXED AIR AND SULFUR WHILE MAINTAINING TURBULENT MIXING UNTIL THE SULFUR IS SUBSTANTIALLY COMPLETELY CONVERTED TO SULFUR DIOXIDE. 